Numerical simulation of heterogeneous propellant combustion by a level set method

In recent years we have completed a number of studies for the modelling and numerical simulation of heterogeneous propellant combustion. A variety of tools have emerged from these studies. The most important are the modelling of propellant morphology, homogenization, and a phase-coupled unsteady three-dimensional combustion model. These tools have been applied to relevant configurations for the study of heterogeneous propellants, including the periodic sandwich, a periodic array of alternating ammonium perchlorate and binder slices, and discs or spheres that are randomly packed. All our previous studies employed a body-fitted grid along the moving interface by means of a mapping technique, since the surface is assumed to be single valued. The computational difficulties are significantly increased when the burning surface undergoes a complex or multi-valued shape. Such complex surfaces can arise, for example, when aluminium particles are embedded in the propellant, or when cracks develop along the propellant surface. In this case the mapping strategy must be abandoned in favour of a more general interface capturing method. One such method, level sets, is explored here. A two-dimensional solver has been developed with this method to simulate heterogeneous propellant combustion. The method involves the formulation of the coupled solid-gas combustion schemes with a level set method, as well as interface and boundary conditions. Several test cases are presented to demonstrate the accuracy of the new method. Results are encouraging and suggest that level set methods can be successfully applied to the study of composite propellant combustion.